Identify the interference geometry

Two coherent point sources $S_1$ and $S_2$ are separated by a small distance $d$.

In interference, the loci of points of constant path difference satisfy $S_2P - S_1P = n\lambda,$ where $P$ is a point on the screen and $n$ is an integer.

Nature of fringes from two point sources

For two point sources, the wavefronts are spherical (or circular in a 2D section). The intersections of constant path-difference surfaces with the screen give the fringe pattern.

When the screen is placed in front of the sources as in the usual arrangement, the loci of constant path difference become circles centered around the point on the screen lying opposite the midpoint of $S_1S_2$.

Hence, the bright and dark fringes appear as concentric circles.

Check the options

• A: points — incorrect, fringes are extended loci, not isolated points.
• B: straight lines — this occurs in Young's double slit arrangement with effectively plane waves at a distant screen, not here for point sources in this geometry.
• C: semi-circles — not the full fringe pattern.
• D: concentric circles — correct.

Final answer

Therefore, the fringes obtained on the screen will be $\boxed{\text{concentric circles}}.$